Transmission control devices adapted as a switch



March 13, 1956 CQOKE ETAL TRANSMISSION CONTROL DEVICES ADAPT'ED AS A SWITCH Filed Afig. 6, 1947 2 Sheets-Sheet 1 mink RRVQQNR QQEEQ iwveriors March 13, 1956 COQKE ET AL 2,738,418

TRANSMISSION CONTROL DEVICES ADAPTED AS A SWITCH Filed Au 6, 1947 2 SheetsShee 2 Ma '29 M United States PaterrfD TRANSMISSION CON TROL DEVICES 1 ADAPTED AS A SWITCH Arthur Halford Cooke, ,OXford, and Herbert Wakefield Banks. Skinner, London,.England, and .Arthur Gowsell ward, Chalk River, ntario,.Canada, assignors to E'liglisWElectric Valve Company Limited, Chelmsford, Eiigla'ndfa company of Great Britain ApplicatiouAugust-6, 1947, Serial No. 766,494 In GreatBritain March 9, H42

sctionl; Public Law'690, August 8, 1946 Patent expires March 9, 1962 201Claims. (Cl.-250-13) This invention relates to'control devices for high frequency"electricaloscillations; and has'for its object to provide a'control clevice adapted toserve as a switch by which-thefidw 0f=high-'frequency energy at-a junction betweentwo"conductors'ti. e. transmission lines and/or or vapour'in which a glow discharge can be excited-said switch serving during such glow discharge to varythe flowv of "energybetween said conductors. The transmission control device may also'be employedso that in its normal or .non-ioniz'ed state, it prevents the flow of power into a line section or otherpart of a transmission system, and upon being ionized it effects theflow of power into .the line section.

.Preferred embodiments of the invention willnow be described with. reference to the accompanying, diagrammatic drawings, inwhichz.

"Figure l'is a schematic longitudinal cross-sectional view of a switch accordingto theinvention, showing the use of the switch in connection with a particularradio application;

Figure 2 isa'view similar .toFigure 1, except .that a waveguide is used in placeof .a transmissionline on .the input, side of'the switch;

Figure?) is across-sectional .view on the line A-.A of Figure '2;

Figure .4'isa detailed'longitudinal cross-sectionalview of. apreferred construction; and

FigureS is.an endelevation of the device shown in Figure .4.

The principle of operation of the switch will now-be described with reference to Figures 1 to 3. The resonator 1 is..associated. in a manner more .fullydescribed .in a later part of 'thespecification with a glass container or envelope 2 carrying the gas and/0r vapour in which the discharge...is excitedypart of the resonator,..terminating in the poles 3, 3a, is located within the container 2, while part is located outside. As shown in Figure-Lethe input side 4 and output .side 5 of atransmission-line (saidsides constituting two conductors or two sections of a transmission system) are coupled by means of loops 6'and 6a to the said outside part of the resonator, whereas as shown in Figures 2.and 3 the input side 4 is replaced by a hollow waveguide 7, rectangular in cross-section, into which theresonator opens directly through an aperture .8." Itwillbeunderstoodthatit desired a waveguide may 2,738,418 Patented Mar. 13, 1956 be .:used: on-cbothzthb :input' and output'zsides; or :one the outputrside only, in conjunction with a transmission line on theinputssideras shown-in Figure .1.: The advantage of using a .waveguide on the input side is that, itemsiderable power is 'beingemployed, it obviates the possibilityythatnwould *existwitha concentric, transmission line, of"sparking toccurring between i the inner :andv outer conducting portions: thereof;

The resonator-.1 is tuned to: thefrequency of the oscillations which rzaretto be transmitted, and is :-thus set :into resonantoscillation by the .energyifed' rintoLit; from the transmission *line ll :or from thewaveguide'fl. -'In1-:.the absence of any glow discharge :this energy passes torfthe outputside'S -with:very little 1oss,-:.but' whena'suchraidischarge isexcited thisexerts apowerful damping :effct uponsthe oscillations. insthe resonator 1 and the amounttof energy passing to the outputrside '5 is: thereby substantially reduced. In the particular construction under 011- sideration the resonator is'constituted' bya'rhumbatron of toroidalform,-as will beseen from Figures 1 and.2;

T he :valueof atoroida'l rhumbatron resonator fol' thfl purpose 'of-thepresentinvention-resides in its high circuit magnification; circuit magnification (which is generally denotedb'y the symbol Q) is definedby-Hensen (Journal of Applied-Physics, vol. 9., October 1938, p: 654) as 1r times'the ratio'of the energy stored in the'circuit to'the energy lost per-half cycle. The necessity for using-a resonator=of.relatively high-Q arisesas follows; If'a resonator of low Q wereemployed, it would be necessary tosuse-relatively tight couplings between the resonator and the-' input and output sidesof the transmission line or' waveguide' 'in order that a suihciently highpercentage of the inputenergy might be transmitted to theoutput side in the absence'of a glow discharge. Under these conditions the damping produced by a glow discharge would have a relatively small effect on-the amount of energy passing-to the 'output side, and the 'etficiency of the device =as aswitchwould "be'smalll If,-however, a resonator-of high Q is-employed, comparatively loose couplings 'sufiice to-transmit energy through'the resonator with=very little loss in the absence of "a glow "discharge, but when such'a discharge is'excited these couplings are insuflicientto transmit power'efliciently 'in view of the heavyyda'mping; Under these conditions most ofthe energy reaching the input coupling is reflected back into the 'transmissio'n line or waveguide, and of the. power entering the'resonator verylittle is transmitted to the output side; so that the device maybe used as a switch ocut-ofii' When 'it'is' desired .that'the switch should operate .automatically, it "is so arranged that theinput-energy shall itself excite the discharge when suchenergy reaches a predeterminedleveLthe supply of energy to the output side then being thereby interrupted for.substantially reduced.

For example',tth'e invention maybe used in connection with beam of ultra-short wave radiation in the form of .a' series of pulses, and 'an associated receiver adapted to pick up the radiations which are reflected. when the transmitted beam encounters the object to be detected. In such systems a common aerial maybe used for both transmission .and reception, and it is then clearly necessary to.protect the receiver, which mayincorporate a crystal or other easily damaged component, from direct excitation. (and damage) 'by the transmitted pulses.

Such protectionmay readily be efiected by the .useot a switch according to the invention as showninFigures l to 3. The transmitter 9. is .connectedtothe aerial-tor equivalentdevice. 10 by a ,transmissionline 11 (Figure ,1) to which the input line 4 is connected, or by the waveguide 7 (Figures 2 and 3) which is coupled directly to the resonator 1 as previously described; in both cases the output transmission line is connected to the receiver 12.

Each transmitted pulse or pulse train, in addition to passing direct to the aerial, serves to excite the glow discharge and thus causes the switch to operate automatically. When such excitation takes plate, the action of the switch is to limit the signal reaching the receiver 12 to a value almost independent of the transmitter power, since the voltage between the poles 3 and 3a of the resonator cannot exceed that at which the discharge passes. As the latter voltage is almost independent of the discharge current, it follows that the voltage between the poles, and consequently the power fed to the output side 5, is almost independent of the input power. The chief efiect of increasing the input power is to increase the discharge current. Most of the input power is reflected back because of the damping of the resonator 1 by the discharge. When no transmission is taking place the discharge ceases, and incoming signals picked up by the aerial 10 are passed on to the receiver 12 with very little loss. The device may obviously be used in this manner in any radio system employing a common aerial for transmission and reception.

For use of the switch non-automatically, the glow discharge may be excited by an external control (6. g. an electrode from which a discharge is caused to excite the glow discharge) applied in any convenient manner as hereinafter described. In this case any signal, however small, is reflected back from the resonator 1 during the discharge instead of being transmitted. Such an arrangement may be used if desired in connection with the radio application previously described, the external control being operated to protect the receiver during the periods of transmission and any other period in which reception is not required. For example, modulation pulses from transmitter 9 may be applied to the electrode 25 to excite the glow discharge during the transmission of each pulse.

A preferred construction according to the invention will now be described with reference to Figures 4 and 5. The resonator here takes the form of a rhumbatron located partly inside and partly outside the glass container or envelope 2, the said container being used as previously described to carry the gas or vapour in which the glow discharge is to be excited. Such a construction may be produced by sealing two copper members 13, 14, formed with central openings 15, between sections of glass tubing 16 which constitute the container or envelope 2, the parts vof members 13, 14, within the tubing being flared towhich are inserted radially through the silvered metal ring 17. Furthermore the copper members 13, 14 may be thermally compensated, so that the gap between their poles 3 remains constant in spite of temperature changes. If a wave guide connection is employed, as described with reference to Figures 2 and 3, the aperture with which the wave guide communicates may be formed in the metal ring 17.

Energy may be fed to and from the switch device in known manner by means of concentric transmission lines whose inner and outer members are connected to the inner members 21, 23' and outer members 22, 22' of terminal devices 23, 23' which constitute respectively plug-andsocket members of a coupling system and are screwed into radial holes in the silvered metal ring 17 at any convenient points. The devices 23, 23 carry coupling loops 6, 6a which lie within the resonator 1 and may be rotated to "adjust the coupling, after which they may be clamped in any desired position by means of lock-nuts (not shown). Alternatively, if a wave guide transmission is employed,

input and output couplings may be made by connecting the sections of the wave guide over suitable openings in the external part of the rhumbatron as previously described with reference to Figures 2 and 3.

The construction described above has a further advantage besides simplicity of manufacture, and ease of tuning and coupling of the resonator. A large volume of gas is contained in the envelope 2, so that cleaning up or absorption of the gas due to the discharge is unimportant. The presence of glass inside the'resonator does not greatly reduce its efiiciency, measured values of Q of 4,000 to 5,000 having been obtained.

The choice of gas or vapour for the filling, which is largely governed by the use to which the control device is to be put, will now be considered. It is clear that the less critical are the conditions under which the control device is required to operate, the wider is the field of choice, but in particular cases any or all of the following factors may be of importance:

(1) In the case where the switch operates automatically, the value or level of input power at which the discharge commences. In the radio application described above the device should pass the most powerful incoming signal which the receiver will normally be required to pick up, and cut off signals more powerful than this.

(2) The time interval between the application of an input power pulse and striking of the discharge. This factor is of importance when the device operates automatically since any delay in the commencement of the discharge may result in the passing on of excessive power to the apparatus to be protected.

(3) The time interval between the cessation of the input power pulse and the cessation of the damping effect, arising from the momentary persistence of effective ionization in the tube. In the radio application referred to it is important that this time-lag (de-ionization time) shall be as short as possible, since the receiver may be required to pick up echoes arriving a few microseconds after the transmitted pulse has been sent out.

In the case of this particular radio application it has been found that water vapour at a pressure of 3 to 10 mm. of mercury gives very satisfactory results, the discharge commencing at a suitable value of input power and the time lag involved in factor (3) being less than half a microsecond as against 10 to 20 microseconds for hydrogen, helium, argon or neon. Rapid recovery is also obtained when water vapour is mixed with other gases such as hydrogen or helium.

A convenient method of ensuring that the time lag covered by factor (2) shall be as small as possible is to arrange that there shall be some ionization in the gap between the resonator poles before the control impulse arrives. It has been found that this priming ionization may be produced by passing a steady discharge between the outside of the resonator and one or more suitable auxiliary electrodes fitted within the glass tube, such as the electrode 25 shown in Figures 1, 2 and 4. A radio-active deposit on such auxiliary electrode or electrodes, or on the inside of the resonator 1 near the poles, will also produce ionization in the gap between the poles; a deposit of mesothorium or radium or their products has been found suitable for this purpose. A source of light shining into the tube also serves to make the discharge begin by producing photo-electrons.

If the switch is to act non-automatically a construction generally similar to that described above may be employed, with the addition of a separate electrode from which a discharge is passed to the rhumbatron for the purpose of interrupting the flow of oscillatory energy. This electrode may comprise a rod (similar to that constituting the electrode 25) which is located axially with respect to the tube 2 and terminates at a suflicient distance from the poles 3 of the rhumbatron to ensure that it does not itself pick up any appreciable amount of the oscillatory energy. For the efiicient operation of the device as aswitch it is desirabi: that the discharge shall be directed as closely as possible to the poles of the rhumbatron, and for this purpose an insulating tube 25a (e. g. of silica or glass) is preferably fitted over the end of the electrode and arranged to extend to the vicinity of the poles. The electrode 25 is connected to a voltage source, represented by battery 26, and the operation of 'the control device may be controlled by switch 27 'whichmay be operated-manually or by any suitable device.

For use at very short Wavelengths .(of the order of 3 centimetres) it may be found convenient to adopt a.construction embodying a rhumbatron located wholly within the glass container. This involves departure from the disc-seal construction described above and is necessitated by the facts:

(1) 'That owing to the very small size of the rhumbatron at such wavelengths said disc-seal construction presents mechanical difliculties, and

(2)"Th'at at these wavelengths the dielectric losses which would result from the presence of glass within-the rhumbatron are considerable. The rhumbatron may convenientlybe connected to sections of a wave guide by openings covered by windows of glass or silica, but if desired a transmission line, suitably sealedthrough the glass container, may be employed.

The cavity resonator constitutes a tuned system in which the spaced metal surfaces surroundingandJforming the twore-entrant poles of the resonator constitute the principal capacity of the system. The resonator is normally tuned 'to the energy supplied to it, but when the gaseous filling becomes ionized, the effective capacity between the two metal pole surfaces is changed tosuch' extent that the system becomes de-tuned.' Also, as already explained, the ionized discharge acts as a damping medium on the waves.

In the arrangements shown in Figures 1 and '2 the transmission control device is employed in a manner to effect transfer of energy from one part of.th"e system to another part when the device is inert, but interrupts the flow of energy during the condition of discharge.

The transmission control device may also be employed so that in its normal or inert state it prevents the transmission of energy from one line section. to another and when ionized would effect the transmission of energy. For example, referring to Figure 1, the transmission control device could be employed to .normally preventv the flow of power from transmitter 9 to the load "by.adjusting the length of the line section 4.. If this line section has a length equal to one-quarter wavelength, substantially no energy will be transmitted fromtransmitter 9to load 10 when the resonator is inert, but transmission wouldoccur when the resonator is ionized. If the line section 4 is a half wavelength long, energy will 'be transmitted from source 9 to load 10 in .the normal or inert state of the resonator but will be interrupted in the ionized state..

Referring to Figures 2 and 3, the resonator is shown connected by a slot in the broad side of the waveguide 7 and constitutes a series element. This arrangement normallyprevents the transfer of power from source 9 to load 10 during the inert state of the resonator but. effects transfer of power during the ionized state. The same operation takes place if the connection of the resonator to the broad side of the wave guide is by a stub having a lengthequal to one-half wavelength. If the connecting stub has a length of one-quarter wavelength, transfer of powerfrom source 9 to load 10 occurs only when the resonator is inert and is interrupted when the resonator is ionized.

By connecting the resonator to the wave guide through aslotformed in the narrow side of the guide longitudinally'thereof, the resonator acts as a shunt element, and would'normally permit the transfer of energy fromsource 9 to load 10 during the inert state but wouldeffectively short circuit the wave guide in-the ionized state. If the connection to the narrow'side of the waveguide is by way of a stub having alength. equal to one-half wavelength, the operation is the same as described,.but if the stub'has a length equal to one-quarter wavelength, .then the operation is reversed from that described.

What is claimed is 1. A transmission control device comprising a cavity resonator having a pair of open ended, re-entrant poles, a sealed envelope of insulating material surrounding said poles within said resonator and containing an ionizable gaseous filling.

2. A transmission control device according to claim 1 and including a priming electrodemounted within said envelope outsideof the cavity of said resonator and extending to a point adjacent one of said re-entrant poles.

3. vAcontrol device comprising a cavity resonator having a pair of spaced poles, at least one of said poles having a central opening forming an aperture in the wall of said resonator, a sealed envelope enclosing the space surroundin'g said aperture on the outside of said resonator, a priming electrode mounted within said envelope and positioned adjacent said aperture, and an ionizable gaseous medium filling said envelope and the space within said resonator.

4. Acontrol device according to claim 3 .wherein said ionizable gaseous medium comprises water vapor at a pressure of 3'10 '10 millimeters. of mercury,

5."Iri combination, an antenna, a high frequency transmitter connected to saidantenna, a receiver, an enclosedfie'ldwave. guide connected between said receiver and said antenna, said wave guide comprisinga cavity resonatortuned to the frequencyof 'said transmitter and enclosing means forprodticirigan ionized gaseous discharge at a;-low vacuum pressure within said resonator for controlling the propagation of 'waves through said guide, and means acting independently of "the wave energy of said transmitter for controlling said last-mentioned means in accordancewith a. predetermined controlling influence.

6. In combination, an enclosed-field wave guide having dimensidhs for and'conducting propagated pulsed wave energy of a .l t determined 'mode, ,a cavity resonator intercepting the.continuity of said wave guide and having entry means for the said'wave energy, said resonator having resonance disruption producing means therein for disrupting resonance and electrically reflecting large pulsesof said pulsed wave energy, but allowing free passage of.received.energy between said large pulses, and a keep-alive electrode for speeding resonance disruption bysaid means.

7.' A tuned 'ionic switch comprising a cavity resonator having conductive inside walls, and having an aperture through a wall thereof, a gas-tight closure mounted in said. aperture and sealing the same, said closure being composedof a material transparent to electromagnetic waves, a pair-of discharge electrodes mounted inside said resonator, and a filling of ionizable gas enclosed by the said walls and closure of the resonator.

8."In combination in a duplex signaling system, a signal wave pulse generator, a signal receiver, a common antenna connected to said generator for radiating the signal .pulses produced by said generator and for picking up incomingwave pulses, means connecting the input of. said receiver to said antenna including a resonant chamber tuned to the frequency of the outgoing wave pulses produced by said generator and .to the frequency of the incoming wave pulses picked up by said antenna, a spark gap connected across .said resonant chamber, adapted to are to effectively short circuit said chamber, and thus to effectively reduce the voltage input tovsaid receiver, in response to the resonant voltage applied .to said chamber by each signal pulse transmitted from, said generator to said antenna, and to remain in the, nonarcingcondition in response to the relatively lower resonant voltage applied to said chamber by the incoming I having Walls with con assert-8 signal pulses l'received y said antenna "during" intervals between transmitted pulses, seas to'p'rovide'a'minimum of attenuation to said incoming pulses in transmission to the receiver during said intervals, and means to maintain a keep-alive discharge adjacent said spark gap during said intervals.

9. In a system for radio transmission and reception over an antenna system common to a transmitter and a receiver, enclosed-fieldwaveguides connecting said transmitter andsaid receiver to' said antenna, a cavity resonator tuned to the frequency of said transmitter and interposed in'the'waveg'uide connectingsaid receiver to the antenna, an electrical discharge gap enclosed in said resonator and located therein at apos'itio'n whereoscillations of the aforesaidfrequency produce voltages greater than the voltages appearingwheresaid resonator is coupled to the waveguide in v vh ieh it is interposed, said dischargeg'apbeiiig prsvidea with means for maintaining an atmosphere. 'ofwatervapor in'said gap at partial vacuum pressure and being adapted to break down and thereby practicallytofshortcircuit said resonator when oscillations of said frequency exceed a predetermined amplitude, and means for establishing a keep-alive discharge adjacent-said dischargegapf f '10.- In" combination, anericlo'sed-field wave guide having 'diniensions li'fof and eb'n'dueti'r i'g propagated 'p'ulsed wave energy ofapredeterrrrinedrmode, a resonator interren g. on,

.tweeni'said M i one of saidgap electrodes 11. A 'IfR boxfconiprismg opposed sparkvgap -e1 said resonator, one,,of said el ect r ode be r, and a keep-alive, electrode '-irioii'rited' withrn "dftnbularpiwarlg-gap electrode. "40

12. A tuned ionic switch comprising a cavity resonator having conductiveljnsidejwalls and 'ha'v'ing'jan aperture therein, a gas-tight closure mounted "insaid, aperture and sealing the lsame,'"said closure ibei'ngjcomposed of a material transparent" t eleetromagneticfwaves, a 'pair of discharge electrodes jmounted inside said resonator on, opposite portions of? the'wallsQthereof, an d afilling of ionizablegas enclosed byl'the said wallsand closure of the resonator. .f.

i 13. A tuned ionic switch comprisinga cavityjresonator tive inside wall surfaces 'and having a glass windowjrn 'a wall thereoffsaid window being hermetically sealed, a pair of discharge electrodes mounted inside said resonator andla filling of ionizable gas enclosed by the"said walls and gas-tight window of the resonator, A

14. An electrical discharge ,device for protecting a sensitive circuit from 'overloads'caused by oscillations of a predetermined frequency including a resonant cavity transformer tuned to""said frequency having low im- '60 pedance input and output circuits and an electrical discharge gap across said resonant transformer at a location of relatively high voltages when said transformer is excited at said frequency adapted to break down when excited oscillations in said transformer exceed a predetermined amplitude, and thereby to short-circuit said input and output circuits of said transformer, said resonant transformer being adapted to transform oscillatory voltages appearing in said" inputicircuit upwardly to said discharge gap and to transform oscillatory voltages. across 70 said gap downwardly to said output circuit, means to maintain the space between said poles at a partial-vacuum pressure to reduce the break-down voltage of said gap, 'and means to m'aintain'a continuous keep-alive discharge -adjacent one of thepoles of said gap.

15. A transmission control device comprising a'eavity resonator having a pair of aligned poles embodied in opposite wall sections thereof, and an ionizable gaseous medium comprising water vapor filling the space between said poles at a pressure greatly less than atmospheric pressure, said resonator being adapted when excited by waves of its resonant frequency to establish an arc'discharge across said poles when said waves exceed a predetermined amplitude.

16;A' transmission control device comprising a cavity resonator containing a pair of aligned poles embodied in opposite wall sections thereof, and an ionizable gaseous medium" comprising a mixture of water vapor and hydrogen filling the space between said poles at a pressure greatly less than atmospheric pressure, said resonator being adapted when excited by waves of its resonanffrequency to establish an arc discharge across said poles when said Waves exceed a predetermined amplitude.

17. A transmission control device comprising'a cavity resonator containing a pair of aligned poles embodied in opposite wall sections thereof, an ionizable gaseous medium filling the space between said poles at apres'sure greatly less than atmospheric pressure, said resonator being adapted when excited by waves of its resonant frequency to establish an arc discharge across said poles when said waves exceed a predetermined amplitude; means for maintaining a continuous keep-alive discharge adjacent one of said poles.

I l8. A transmission control device comprising aIca'vity resonator having apair of aligned poles embodied inro'pposite wall sections thereof, an ionizable gaseous medium comprising water vapor filling the space between said poles at a pressure greatly less than atmospheric 'p ressure, said resonator being adapted when excited \iv'a'ves of its resonantfrequency to establish an arc d barge 1' v l .0 across said poles when said waves exceed a predeterm ned I amplitudfi, and means for maintaining a continuousik'eepalive discharge adjacent one of said poles.

19. An electrical discharge device for protecting ia sensitive circuit from overloads caused by oscillationsjof a predetermined frequency including a resonant cavity transformer tuned to said frequency having low impedance input and output circuits, an electrical discharge gap across said resonant transformer at a location of relatively high voltage when said transformer is excited at said frequency and adapted to break down when excited oscillations in'said transformer exceed a predetermined amplitude and thereby to short-circuit said input and output .circuits of said transformer, said resonant transformerbeing adapted to transform oscillatory voltages appearing in Said input circuit upwardly to said discharge gap and to transform oscillatory voltages across said gap downwardly for energy transfer to said output circuit, and means for maintaininga partial vacuum in the space surrounding said electrical discharge gap, said means including at least one wall portion of non-conducting material sealed to the structure of said resonator at a location such that relatively low voltage stresses are caused to occur in said wall portion as the result of said oscillations. I

20. In combination in a duplex signalling system, a signal wavepulse generator, a signal receiver, a common antenna connected to said generator for radiating, the signal pulses produced by said generator andfor picking up incoming wave pulses, means connecting the inputof said receiver to said antenna including a resonant chamber tuned to the frequency of the outgoing wave pulses produced by said generator and to the frequency of the incoming wave pulses picked up by said antenna, a. spark- "gap connected across said resonant chamber, adapted to are to effectively short-circuit said chamber, and lthus'to eliectively reduce the voltage input to said receiver, in

response to the resonant voltage applied to said chamber by each signal impulse transmitted from said generator to said antenna, and toremain in the non-arcing condition response to the relatively lower resonant voltage applied an-K References Cited in the file of this patent UNITED STATES PATENTS Girardeau Aug. 20, Dallenbach et a1. Apr. 28, Steudel Mar. 7, Richmond July 2, Jenks Oct. 1, Evans Nov. 5, Okress Feb. 18, Tuller Apr. 5, Montgomery Aug. 30, Kandoian Oct. 25,

FOREIGN PATENTS Great Britain June 10, 

